1. Field of the Invention
This invention generally relates to the field of drill bits for tunneling through soft materials and specifically relates to a spring bore drill bit for tunneling in a generally straight line through soft earth or soft or rotten wood in order to lay underground cables such as fiber optic cables.
2. Prior Art
The inventor is unaware of any drill bits specifically developed for the task of drilling in a generally straight line through soft earth or soft or rotten wood which are maneuverable in a typical manhole environment. Currently, this task is performed by two methods, the use of larger scale underground rotary tunneling mechanisms and the use of smaller scale blunt ended rod means powered by brute force.
In the past, utility cables were installed by several methods, including merely laying the cable in a dirt trench and covering the cable with dirt and by installing a wooden conduit underground and laying the cable within the wooden conduit. Over time, as the cables become aged or obsolete, the cables need to be replaced. Current fiber optic technology allows the use of a fiber optic cable of approximately the same diameter as the old cables, such as, for example, telecommunications or electric cables, yet the fiber optic cables carry many times more information. Therefore, the fiber optic cables can be laid in approximately the same space as and in place of the old cables. However, after the old cables are removed from their beds, a new tunnel needs to be created or the dirt or wood conduit generally needs to be reamed in preparation for the insertion of the new cable.
Various methods and apparatuses for creating cable tunnels or reaming the dirt or wooden conduit are shown in the prior art. The two methods of which the inventor is most familiar include the use of various drill bits and drilling apparatuses such as U.S. Pat. No. 4,026,371 to Takata, et al., U.S. Pat. No. 4,856,600 to Baker, et al., and U.S. Pat. No. 4,674,579 to Geller, et al. However, each of these prior art patents generally are complex mechanical devices having separately rotatable bit heads, water jets, and/or steering mechanisms. Rigid rods also can be used to create tunnels or to ream conduits by brute force.
There also are various methods for reaming out soft materials, generally from pipes or conduits. For example, the well known Roto-Rooter brand equipment comprises a generally snake-like flexible driving mechanism and a generally spring-like flexible reaming head. The flexible spring-like nature of the reaming head allows the reaming head to travel around bends in pipes and to force soft material toward the back of the reaming head due to the helical nature of the spring comprising the reaming head. However, such a reaming head is inappropriate for traveling through materials harder than typical waste sludge and, due to the flexible nature, are difficult to keep traveling in a straight line without some type of wall to guide them.
When tunneling through soft dirt and when reaming prior existing conduits, it is common to encounter and possibly contact existing cables with the reaming device. Many times these cables are not encased in a hardened outer coating and are easily damaged upon contact. Many of the prior art tunneling and reaming devices, such as drills and rigid rods, have hardened and/or sharp-edged heads which easily can cause damage to existing cables.
Accordingly, it can be seen that there is a need for a mechanically simple drill bit mechanism for use in tunneling through soft earth and soft and rotten wood which is rigid enough to travel in a straight line, yet which will have a bit head which will not damage prior existing cables upon contact. The present invention is directed to accomplish this need.